Advances made in the chemical composition of plastic film has produced film with new physical characteristics including resistance to lateral and longitudinal stretching. The lateral resistance of the plastic film produces increased stress upon the tentering clips, located on opposite sides of the tentering frame in endless chains, which stretch the film to reduce the film thickness.
The additional stress causes distortion between pivotally connected clips disclosed in the prior art. The distortion is due to the length of the distance between the plane in which the film is gripped and the plane passing through the point of contact of the stress rollers with the tentering frame rail face.
The problem presented is the need to increase the strength of both the tenter clip and the tenter base forming the tentering chain and reduce the space between adjacent clips to avoid juxtapositioning of adjacent clips. The further problem presented is the need to increase the strength of the drive sprocket which must pull a greater load due to the increased frictional contact of the stress rollers with the rail face. The cost of manufacture of the new and improved structure had to be held to a minimum.
The present invention is considered to be an improvement over U.S. Pat. Nos. 3,058,191, 3,580,451, 3,142,108, 3,638,289, 3,457,608, 3,748,704, 3,469,291, 4,134,189, 3,555,637, and French Pat. No. 1,337,600 dated Aug. 1963.